To a medium bowl, add the thinly sliced chicken, lime juice, olive oil, agave nectar, ancho chili powder, ground cumin, smoked paprika, & garlic powder. Season with S&P as desired. Stir to combine well & coat chicken. Set aside to marinate for 10-15 minutes, or cover & marinate up to 12 hours in the refrigerator.
Heat 1 Tbsp olive oil in a large skillet over medium-high heat. Once hot & shimmering, add half of the marinated chicken. Cook 5-6 minutes, flipping halfway through until the chicken is cooked through & begins to brown. Transfer the cooked chicken to a plate or bowl & set aside. Repeat with the remaining chicken – there should be no need to add extra oil between batches.
Add the sliced bell pepper & onion to the skillet. Season with garlic powder, a heaping 1/2 teaspoon kosher salt, & ground black pepper as desired. Cook, stirring occasionally until softened slightly, about 4-5 minutes – the veggies should be tender-crisp. Squeeze the remaining lime juice over the fajitas veggies & toss to combine. Remove the skillet from the heat.
Add the chicken back into the skillet, tossing to combine it with the fajitas veggies well, then serve immediately as desired. Enjoy!